As the largest Opposition party in Westminster, Labour is responsible for holding the UK Government to account on Brexit. In order to do this effectively, they need a policy of their own, especially in relation to membership of the customs union and single market. If Labour wasn't clear about whether they wanted in or out of these two treaties then it would make it impossible for them to try to influence government policy. Plaid Cymru's position is clear: we want to stay in the single market and customs union. So what is Labour's policy on membership of these?